The present invention relates to a device for separating dirt and debris in flowing media by making use of centrifugal forces, said device comprising a separation chamber and a dirt collection chamber connected with said separation chamber by at least one dirt discharge opening. The device is particularly suited for purifying cooling medium used to cool the parts of a fluid flow machine, such as for example, the guide vanes of a turbine plant.
Adequate and reliable cooling of the parts of a fluid flow machine is an important aspect in the operation of such a fluid flow machine. Modem, high-temperature gas turbines require a sophisticated cooling system in order to achieve a high degree of efficiency, in particular for cooling the highly stressed turbine blades. For this reason, the turbine blades are interpenetrated with cooling ducts or hollow spaces that form cooling ducts, through which a cooling medium, in particular cool air flows when the machinery is in operation. Generally, numerous cool air bores are provided on the front edge of the turbine blades in the approach flow region, through which the cooling medium is able to pass from the interior of the blades outwardly. In this region a film of cool air forms on the surface, which protects the turbine blades from excessive heat build-up. Similarly, corresponding cool air bores are also located on the back edge of the turbine blades.
In many cases the cooling medium is formed by a portion of air that is compressed by, or is conducted past, the compressor stage and is conveyed to the cooling ducts through one or more supply ducts.
A problem that presents itself during operation of such cooling systems in a fluid flow machine is the clogging of the cooling ducts or cool air bores by dirt or dust particles drawn from the outside air or from parts of the fluid flow machine disposed upstream of the cooling ducts, and which are transported with the cooling medium into the cooling ducts. The clogging of individual cooling ducts or cool air bores may result locally in substantial thermal stress to the parts being cooled, to the point of damaging them.
To eliminate or reduce the danger of clogging it is known to arrange separators, such as cyclones, within the cooling system for separating dirt and dust particles from the cooling medium. In these separators swirls are generated in the cooling medium by means of which the dirt and dust particles due to their inertia are separated from the cooling medium and are carried off through a separate dirt discharge opening.
The use of separators of this type in the form of an axial cyclone is described in German patent publication DE 198 34 376 A1. Here, the cool air passing from the compressor stage is conducted prior to intake by such an axial cyclone into the first guide vane of the turbine stage. The cyclone is designed internally with a swirl generator that imparts a swirl in the cool air flow, as a result of which the slower-moving dust and debris particles strike the wall of the cyclone and drop downwardly. At the bottom of the cyclone they are carried off through corresponding discharge ducts.
The discharge ducts lead to areas of the gas turbine that do not react sensitively to dust, debris and moisture droplets or other impurities. For discharging dirt particles, however, a portion of the cool air is consumed which is then no longer available for the cooling of sensitive components. Such a continual loss of valuable cool air is undesirable, since as a rule the cool air is costly to compress and in a number of cases has been re-cooled outside the gas turbine. The loss of said portion of cool air negatively impacts the operating efficiency of the plant and also reduces the cooling effect on the dirt-sensitive components of the gas turbine.
To eliminate the continuous loss of cooling medium, it is also known to equip the dirt separator with a dirt collection chamber in which the separated dirt and debris particles temporarily accumulate. The dirt collection chambers may then be emptied when the plant is not in operation. An example of an embodiment of such a device for separating dirt and debris is shown in FIG. 1 in the form of a reverse cyclone. FIG. 1 shows a separation chamber 1 which generates by virtue of its conical shape a swirl flow in the cooling medium. The cooling medium to be cleaned enters tangentially into the separation chamber 1 through inlet opening 9. Within the swirl flow the dirt and debris particles entrained in the cooling medium are hurled outwardly by centrifugal force against the walls of the separation chamber, where they lose their kinetic energy due to friction with the walls, then drop through dirt discharge opening 2 to the bottom or onto the tip of the conically shaped separation chamber 1 and into the underlying dirt collection chamber 3. In the center of separation chamber 1 an upwardly directed reverse flow is formed, by means of which the purified cooling medium once again exits the device through the central outlet opening 10.
Because of the limited space inside a fluid-flow machine, effort is made to design dirt collection chamber 3 as compactly as possible. However, this may cause a relatively large portion of the particle flow entering dirt collection chamber 3 to flow back again into the separation chamber. Moreover, it is desirable if dirt separators of this type are capable of being installed in any desired position in the fluid flow machine, e.g. horizontally or upside down. Such modified positions may also cause a relatively large portion of the dirt and debris particles to exit the dirt collection chamber, and thus remain entrained in the cooling medium.
Based on the aforementioned prior art the object of the present invention is to provide a device for separating dirt and debris having a dirt collection chamber, in which the danger of backflow of dirt and debris particles from the dirt collection chamber into the separation chamber is reduced.
The object is achieved with the device according to claim 1. Advantageous embodiments of the device are set forth in the dependent claims. Claims 11-14 contain additional preferred uses of the present device in a fluid flow machine.
The present device for separating dirt and debris in flowing media operates in a known manner by making use of centrifugal force. Said device has a separation chamber and a dirt collection chamber connected with the separation chamber by at least one dirt discharge opening. Arranged in the region of the dirt discharge opening within the dirt collection chamber of the present device are one or more flow guide elements, which make the backflow of dirt and debris particles into the separation chamber difficult. The flow guide elements may for example originate from the side walls of the dirt extraction chamber or from the rim of the dirt discharge opening.
It was recognized in accordance with the present invention that the arrangement of suitable flow guide elements in the region of the dirt discharge opening within the dirt collection chamber could significantly reduce the danger of backflow of dirt and debris that had been separated off. Such flow guide elements have a dual function. First, they stabilize within the dirt collection chamber a swirl flow that is generated to separate particles in the separation chamber; hence because the swirl flow is also maintained within the dirt collection chamber, the dirt and debris particles remain trapped against the sidewalls. Second, they also define a physical barrier against the backflow of separated particles into the separation chamber.
This supplemental arrangement of flow guide elements in the area of the dirt discharge opening can significantly reduce the danger of backflow of dirt and debris in relatively small dirt collection chambers as well. Moreover, devices designed in this manner are more easily mounted in fluid flow machines in different orientations, without reducing functional capacity.
In one advantageous embodiment, at least one flow guide element is supported by a conical body that tapers in the direction of the dirt discharge opening, and which projects from the side of the dirt collection chamber opposite the dirt discharge opening. The tip of said conical body protrudes into the center of the dirt discharge opening. The swirl or turbulent flow generated in the separation chamber carries over in similar manner into the dirt collection chamber. Furthermore, the central conical body forms an added physical barrier against the flow of separated dirt or debris back into the separation chamber.
In another advantageous embodiment a flow guide element in the form of a ring shaped collar extends from the rim of the dirt discharge opening into the dirt collection chamber. Thus, a particularly effective hold-back system is realized, in particular when combined with a conical interior body as provided in the aforementioned embodiment.
In yet another advantageous embodiment, a flow guide element disposed in the region of the dirt discharge opening is designed in the form of a ring composed of guide vanes that are aligned with the swirl flow formed in the separation chamber. These guide elements thus also transmit the swirl flow formed in the separation chamber into the dirt collection chamber. They may cover the entire dirt discharge opening, or they mayxe2x80x94particularly in combination with a conically shaped interior bodyxe2x80x94cover the slot opening that remains between the interior body and the rim of the dirt discharge opening. Guide vanes of this type form an especially effective barrier against the backflow of dirt and debris from the dirt collection chamber.
Preferably, the dirt collection chamber of the present device has at least one dirt discharge duct through which accumulated dirt and debris may be carried off via a shut-off valve at set time intervals. Preferably, this duct is connected to a region of the fluid flow machine that is lower in pressure than the dirt collection chamber. Alternatively, said duct may be connected to the environment or outside air. By this means, dirt is automatically discharged when the valve is opened due to the pressure differential. The discharge of dirt is preferably carried out only at set intervals during operation of the fluid-flow machine so that the resultant loss of cooling medium is kept very minimal. In a variant mode of operation the valve is opened during shut down of the machine in order to empty the dirt collection chamber.
It is understood that for purposes of reducing the loss of cooling medium, these modes of operation can also be implemented in dirt separators which have dirt collection chambers and at least one dirt discharge duct fitted with a shut-off valve, but which have no flow guide element according to the present invention.
In a further use, multiple devices of the present kind are arranged in a fluid flow machine, and the dirt discharge ducts of all or of individual groups of dirt collection chambers are joined together and drained by way of a common valve. This facilitates the functioning and control of the valves during the emptying process.
The present device is preferably used by installing it in a gas or steam turbine plant for purifying the cooling medium, especially cool air that is conveyed to the guide vanes of the plant.